There is no ideal host rock, which garantuees by its retention capability minimal hazardous consequences for population and environment from deep geological HLW repositories for 1 Mio years!
Therefore new attention should be given to the long-term retention capability of the waste package.
The best solution for the long-term immobilization of high-level waste seems to be the encapsulation in high-tech ceramics, preferably sintered silicon carbide in combination with potting, know as SIAMANT@ BASIS CONCEPT.
Ceramic encapsulation is more than just increasing redundancy of multiple barrier concepts. SSiC encapsulation has the potential to contribute to a new quality of the solution for the back-end problem in the nuclear fuel cycle.
Through SIAMANT@ waste packages even less favourable repository sites become licensable!